BBC is reporting that the suspect "posted an image of a pistol with three sets of bullets"
https://www.bbc.com/news/world-asia-51427301
I don't know if that means three bullets, three speed loaders, three magazines, three boxes of bullets, or what.
According to this only the wealthy and well-connected can carry in Thailand:
https://www.quora.com/What-are-the-gun-laws-in-Thailand-like